<template>
  <div class="pagination">
    <button :disabled="pageNo ==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>

    <button v-if="startNumAndEndNum.start >1" @click="$emit('getPageNo',1)" :class="{active:pageNo == 1}">1</button>

    <button v-if="startNumAndEndNum.start >2">···</button>

    <!-- 中间部分 -->
    
    <button  
    v-for="(page,index) in startNumAndEndNum.end" 
    v-show=" page >= startNumAndEndNum.start"
    @click="$emit('getPageNo',page)"
    :key="index" 
    :class="{active:pageNo == page}"
    >{{page}}</button>

    <button  v-if="startNumAndEndNum.end <totalPage - 1">···</button>
    <button  v-if="startNumAndEndNum.end <totalPage" @click="$emit('getPageNo',totalPage)" :class="{active:pageNo == totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',totalPage+1)">下一页</button>
    
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    //父组件传递给子组件的数据   当前页数、每页数据量、总数据、连续页数
    props:['pageNo','pageSize','total','continues'],
    //计算属性
    computed:{
      //计算总页数
      totalPage(){
        //向上取整
        return Math.ceil(this.total/this.pageSize);
      },
      //开始页数和结束页数
      startNumAndEndNum(){
        const {continues,pageNo,totalPage} = this;
        //声明两个变量存放开始结束页数
        let start = 0 , end = 0;
        //连续页码数字为5，即至少5页，如果不足五页，则显示不正常
        //页码少于5页，不正常现象
        if(continues > totalPage){
          start = 1;
          end = totalPage;
        }else{
          //正常现象，页码大于5
          //开始页数
          start = pageNo - parseInt(continues / 2);
          //结束页数
          end = pageNo + parseInt(continues / 2);
          //把不正常现象纠正：start数字出现0或负数
          if(start<1){
             start = 1;
             end = continues 
          }
          //纠正end大于总页数的情况
          if(end > totalPage){
            end = totalPage;
            //开始页码=总页码减去连续页码+1
            start = totalPage -continues +1; 
          }
        }
        return {start,end}
      }
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
    text-align: center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
  .active{
    background: skyblue;
  }
</style>